There are numerous standards for encoding numeric and other information in visual form, such as the Universal Product Codes (UPC) and/or European Article Numbers (EAN). These numeric codes allow businesses to identify products and manufactures, maintain vast inventories, and manage a wide variety of objects under a similar system and many other functions. The UPC and/or EAN of the product is printed, labeled, etched, or otherwise attached to the product as a dataform.
Dataforms are any indicia that encode numeric and other information in visual form. For example, dataforms can be barcodes, two dimensional codes, marks on the object, labels, signatures, signs etc. Barcodes are comprised of a series of light and dark rectangular areas of different widths. The light and dark areas can be arranged to represent the numbers of a UPC. Additionally, dataforms are not limited to identifying products. They can be used to identify important objects, places, etc.
Direct Part Marking (DPM) is an important way to permanently mark objects for identification. For example, the automotive and aerospace industries have decided to use DPM dataforms to identify their products. In DPM, the surface of the object is modified to include dataforms, such as, for example, barcodes, two dimensional codes, etc. One exemplary method of marking is dot-peening, in which the surface of the object is impacted by a peening device, such as, for example, a stylus. Each impact creates a “crater”, and a collection of craters can be used to form patterns that represent dataforms such as a DataMatrix™. The crater may also have a slightly raised rim around its circumference created by the material displaced during the peening process. Other methods to create surface profile modifications comprise laser etching, chemical etching, and electrochemical etching.
FIG. 1 illustrates an exemplary dot-peened dataform 102. The circles represent craters on the surface of the object. The craters are arranged in an array that represents information. The dataform 102 can comprise information regarding the manufacturer, the UPC, the time, date and location of manufacture, etc. This information can be used for inventory, accountability, identification, recalls, etc.
In some DPM applications there is no intrinsic contrast at the site of the marking between the surface of the object and the dataform, when scanning DPM dataforms, scanning devices use the creation of highlights and/or shadows on the surface of the object to properly detect the dataform. Two ways to detect the dataform are to use bright field illumination and dark field illumination.
In an exemplary bright field illumination implementation, an extended light source is used to create a broad beam illumination. When an image of the dataform is captured using bright field illumination, the background surface tends to show up bright, while the marked features, i.e., the dataform, shows up dark. In one exemplary dark field illumination implementation, a narrow beam illumination is created by a set of point light sources rather than a single point light source. When using dark field illumination, the dataform is lit up brightly, while the surface of the object is left in relative darkness.
Known scanners that use this dark field illumination method implement point light sources that are symmetrical about the optical system of their camera. For example, one known scanner has a ring of 9 light emitting diodes (LEDs) that illuminate the dataform at the same time, while other scanners have a diffusing lightpipe that has a cylindrical extrusion that is designed to enclose the mark being scanned.
Other handheld scanners comprise two light sources that illuminate a dataform from the left and right sides simultaneously, while a proposed print-quality standard of DPM suggests the use of four point light sources 90° from each other and at 45° from the surface of the dataform, with the camera of the scanner situated at a perpendicular direction that passes through the center, or in other words, along an axis that is symmetrical with respect to the four light sources. Unfortunately, symmetric illumination of DPM dataforms can make the image difficult to decode when the dataform is illuminated at certain angles.
In another dark field illumination implementation, glancing illumination is used to brightly illuminate the dataform. Glancing illumination is illumination that strikes the dataform at an extreme angle. Light that strikes the surface of the object glances off, while light that strikes the craters of the dataform is reflected back to the scanner. A known handheld DPM scanner that provides glancing illumination comprises a clear cylindrical pipe. A first open end of the pipe is attached to the head of the scanner and a second end of the pipe contains LEDs. The LEDs provide a broad illumination and are broken into four equal groups. All the LEDs may be used at once or one group at a time may be used. In an exemplary operation of the scanner, a user places the second end of the pipe directly over a dataform to provide glancing illumination. Unfortunately, in order to make sure the illumination is glancing the user must place the pipe directly on or very close to the surface of the object. In addition, the field of view of the camera does not extend far beyond the second end of the pipe. Thus, the glancing scanner is not effective when a target dataform is surrounded by an obstruction, or if the dataform is recessed in a sunken area of an object since the illumination is no longer glancing and the field of view of the scanner may not extend that far.
Additionally, known DPM scanners with built in illumination subsystems, such as the ones described above, are often large and/or fragile. Accordingly, a need exists for DPM scanners with sturdy illumination subsystems that do not have to be placed directly over a target dataform and can produce images that are easier to decode.